Pumps are used in many industrial processes to force liquid-state fluid from a first location to a second location. Some processes require pumps that are able to discharge fluid under high pressure, 100 psi or more, and to discharge relatively large amounts of fluid, 20 gpm or more. For example, such pumps are employed in reverse osmosis systems, waste and fresh water processing plants and in pressure cleaning systems. In the past, a number of different pumps have been developed that cause the fluid to develop the requisite pressure head required to cause it to flow from its source to a destination location. Many pumps include one or more piston units that provide the pumping force that causes liquid movement.
While current pumps work reasonably well, there are some disadvantages associated with their use. Many of the current pumps include one or more linkage members that connect the pistons to the complementary drive motors. These linkages need to be lubricated and the heat they generate during use must be extracted. Consequently, it is necessary to supply many current pumps with lubricating systems in order to both lubricate and cool the internal components of the pumps. It is even necessary to provide some pumps with supplemental cooling systems to prevent the internal components of these pumps from overheating. Having to add these lubricating systems and cooling systems can significantly add to the overall cost of providing a pump. Moreover, these sub-systems, like most mechanical systems, need to be subject to periodic maintenance and have the potential to malfunction.
Moreover, many pumps are designed so that the length that their pistons travel, i.e., the piston stroke, is relatively long. For example, it is not uncommon for a piston in a conventional pump to have a 3 inch stroke. If the pump is operated at 400 RPM, the rate at which a 50 horsepower pump can operate, the total travel of an individual piston works out to approximately 2400 inches/min, (the piston stroke doubled and multiplied by the strokes per minute). Pistons traveling at these rates of speed can impose significant wear on both the pistons themselves and the associated components, the packing and the throw bushings. This high-speed piston travel also inevitably generates a significant amount of heat which further contributes to the wear of the pistons and associated components. Collectively, this heat generation and wear increase the amount of maintenance that needs to be performed on a pump.